Apple trees, even neglected ones, generally can be completely renovated with 5-6 years of knowledge-able pruning. It may be unrealistic to expect a good crop for several years, until you get the trees back into shape. A good place to start is by removing any dead or damaged branches in late winter while the tree is still dormant. Next take out crossing branches and those growing inward, downward, or strongly upright. Thin out branches growing directly on top of one another. However, you should remove no more than about 1/4 of the branches each year. For more detailed instructions, get a book about fruit growing and follow the pruning diagrams, or check with your county extension service for bulletins on pruning fruit trees.